(1) Field of the Invention
The present invention relates to a liquid crystal display device, and in particular, to a liquid crystal display device having a photosensor for measuring the amount of backlight.
(2) Description of the Related Art
In recent years, some liquid crystal display devices have a photosensor in the backlight unit or in the liquid crystal display panel in order to maintain the liquid crystal display device at an arbitrary brightness. These liquid crystal display devices have such a structure that the amount of light from the light source is controlled and the backlight for illuminating the liquid crystal display panel from the backlight unit provided on the rear side of the liquid crystal display panel is kept constant.
In these liquid crystal display devices, the photosensor is generally provided in a periphery portion of the liquid crystal display device or on the rear side of the light guide plate in order to nullify the effects of the external light entering through the display surface of the liquid crystal display panel.
Examples of the liquid crystal display device where a photosensor is provided on the rear side include the illumination device and the display device in JP 2000-315596A. In the illumination device and the display device in JP 2000-315596A, a brightness sensor (photosensor) is provided at the bottom of the casing (lower frame) for containing a light guide plate and a discharge lamp that works as the light source, and the brightness of the backlight is measured in the structure.